1,051 research outputs found
Effects of Magnetic Field on Josephson Current in SNS System
The effect of a magnetic field on Josephson current has been studied for a
superconductor/normal-metal/superconductor (SNS) system, where N is a
two-dimensional electron gas in a confining potential. It is found that the
dependence of Josephson currents on the magnetic field are sensitive to the
width of the normal metal. If the normal metal is wide and contains many
channels (subbands), the current on a weak magnetic field shows a dependence
similar to a Fraunhofer-pattern in SIS system and, as the field gets strong, it
shows another type of oscillatory dependence on the field resulting from the
Aharonov-Bohm interference between the edge states. As the number of channels
decreases (i.e. normal metal gets narrower), however, the dependence in the
region of the weak field deviates from a clear Fraunhofer pattern and the
amplitude of the oscillatory dependence in the region of the strong field is
reduced.Comment: 14 pages, 9 figure
Electron focusing, mode spectroscopy and mass enhancement in small GaAs/AlGaAs rings
A new electron focusing effect has been discovered in small single and
coupled GaAs/AlGaAs rings. The focusing in the single ring is attributed solely
to internal orbits. The focusing effect allows the ring to be used as a small
mass spectrometer. The focusing causes peaks in the magnetoresistance at low
fields, and the peak positions were used to study the dispersion relation of
the one-dimensional magnetoelectric subbands. The electron effective mass
increases with the applied magnetic field by a factor of , at a magnetic
field of . This is the first time this increase has been measured
directly. General agreement obtains between the experiment and the subband
calculations for straight channels.Comment: 13 pages figures are available by reques
On the Non-invasive Measurement of the Intrinsic Quantum Hall Effect
With a model calculation, we demonstrate that a non-invasive measurement of
intrinsic quantum Hall effect defined by the local chemical potential in a
ballistic quantum wire can be achieved with the aid of a pair of voltage leads
which are separated by potential barriers from the wire. B\"uttiker's formula
is used to determine the chemical potential being measured and is shown to
reduce exactly to the local chemical potential in the limit of strong potential
confinement in the voltage leads. Conditions for quantisation of Hall
resistance and measuring local chemical potential are given.Comment: 16 pages LaTex, 2 post-script figures available on reques
Hypermethylation of ribosomal DNA in human breast carcinoma
We examined the methylation status of the transcribed domain of ribosomal DNA (rDNA) in 58 patients with breast cancer. The mean percent of methylation was significantly higher in breast tumours than that of normal control samples (P< 0.0001). This increased rDNA methylation was associated with oestrogen receptor non-expression (P< 0.0273) and with moderately or poorly differentiated tumours as compared to well differentiated tumours (P< 0.0475). Our results suggest that rDNA can be a useful marker for monitoring aberrant methylation during breast tumour progression. © 2000 Cancer Research Campaig
Far-infrared induced current in a ballistic channel -- potential barrier structure
We consider electron transport in a ballistic multi-mode channel structure in
the presence of a transversely polarized far-infrared (FIR) field. The channel
structure consists of a long resonance region connected to an adiabatic
widening with a potential barrier at the end. At frequencies that match the
mode energy separation in the resonance region we find distinct peaks in the
photocurrent, caused by Rabi oscillations in the mode population. For an
experimental situation in which the width of the channel is tunable via gates,
we propose a method for reconstructing the spectrum of propagating modes,
without having to use a tunable FIR source. With this method the change in the
spectrum as the gate voltage is varied can be monitored.Comment: Submitted to Phys. Rev.
Far-infrared absorption in parallel quantum wires with weak tunneling
We study collective and single-particle intersubband excitations in a system
of quantum wires coupled via weak tunneling. For an isolated wire with
parabolic confinement, the Kohn's theorem guarantees that the absorption
spectrum represents a single sharp peak centered at the frequency given by the
bare confining potential. We show that the effect of weak tunneling between two
parabolic quantum wires is twofold: (i) additional peaks corresponding to
single-particle excitations appear in the absorption spectrum, and (ii) the
main absorption peak acquires a depolarization shift. We also show that the
interplay between tunneling and weak perpendicular magnetic field drastically
enhances the dispersion of single-particle excitations. The latter leads to a
strong damping of the intersubband plasmon for magnetic fields exceeding a
critical value.Comment: 18 pages + 6 postcript figure
The spin-orbit interaction as a source of new spectral and transport properties in quasi-one-dimensional systems
We present an exact theoretical study of the effect of the spin-orbit (SO)
interaction on the band structure and low temperature transport in long
quasi-one-dimensional electron systems patterned in two-dimensional electron
gases in zero and weak magnetic fields. We reveal the manifestations of the SO
interaction which cannot in principle be observed in higher dimensional
systems.Comment: 5 pages including 5 figures; RevTeX; to appear in Phys.Rev.B (Rapid
Communications
- …